The invention constitutes an improvement over the apparatus shown in U.S. Pat. No. 3,882,678 which relates to connecting a reserve pump into a steering booster system in the event of failure of the main pump, or dropping of pressure. Inasmuch as the pressure flow consumer such as a servomotor is operated at a pressure which is maintained below a certain pressure limit, limiting or regulating valves are used. Also, in such systems wherein a main and reserve pump are used a signal device is generally required to indicate that the system is operative.
In the several prior art arrangements the apparatus utilizes a pressure differential, for example, a metering throttle for operating a valve piston and/or signal means. The several components are generally connected in series so that losses of pressure become cumulative.
For proper operation of series connected valves and indicators a precise sequence of connection of components is required. Such precision of adjustment and relationship of the components requires very close tolerances and, accordingly, high manufacturing expense is involved.